Spiral-wound membrane filtration elements consist of a laminated structure comprised of a membrane sheet sealed to or around a porous permeate spacer which creates a path for removal of the fluid passing through the membrane to a central tube, while this laminated structure is wrapped spirally around the central tube and spaced from itself with a porous feed spacer to allow axial flow of the fluid through the element. While this feed spacer is necessary to maintain open and uniform axial flow between the laminated structure, it is also a source of flow restriction and pressure drop within the axial flow channel and also presents areas of restriction of flow and contact to the membrane that contribute significantly to membrane fouling via biological growth, scale formation, and particle capture.
Improvements to the design of spiral wound elements have been disclosed by Barger et al and Bradford et al., which replace the feed spacer with islands or protrusions either deposited or embossed directly onto the outside or active surface of the membrane. This configuration is advantageous in that it maintains spacing for axial flow through the element while minimizing obstruction within the flow channel. It also eliminates the porous feed spacer as a separate component, thus simplifying element manufacture. Patent publication number US2016-0008763-A1 entitled Improved Spiral Wound Element Construction teaches the application of printed patterns on the back side of the active surface of the membrane sheet, or directly on the surface of the permeate spacer.
The following references, each of which is incorporated herein by reference, can facilitate understanding of the invention: U.S. Pat. Nos. 3,962,096; 4,476,022; 4,756,835; 4,834,881; 4,855,058; 4,902,417; 4,861,487; 6,632,357; and US application 2016-0008763-A1.